09 April 2012

Red is sexy but not sexual

The Methods section of most papers is the least read part of the paper. You can see this in how some journals print the Methods in a tiny point size. Others have taken to putting the section at the end of the paper, so as not to disrupt the narrative flow with details.

Occasionally, you get a paper – usually in your field – where you need to read the Methods section closely to understand a paper enough to criticize or replicate.

Rare indeed are papers where the story is so unusual that I think, “I have absolutely got to read that Methods section!”

A new paper by Johns and colleague marks the first time I thought, “I have to read those Methods,” and “These Methods should come with an NSFW warning.”

It’s about the colour red.

Red seems to affect us in a way that other colours don’t (Elliot et al. 2007, Hill & Barton 2005). Case in point:

These head-turning dresses would not be the show-stoppers they are if they were beige.

Red is sexy.

If that picture doesn’t convincing you, check out Elliot and Niesta, 2008 and go through the data to your heart’s content.

Johns and colleagues test an hypothesis for why red on women looks so attractive to me. The hypothesis is that red is sexy because it reminds men of... lady parts.

An obvious objection to this idea is that t external sex organs of women are not red in the way that the dresses above are red. The hypothesis is a more subtle, however. One version of the hypothesis is that as females are approaching ovulation, the vulva becomes more red than is is at other points in the cycle.

If this “red is code for female sex organs” hypothesis is true, you might predict that men would judge female genitals as more attractive as they became more red.

The Methods section does not disappoint.

Explicit images of anatomically normal, un-retouched, nonpornographic, similarly-orientated female genitals were surprisingly difficult to obtain... We selected photographs that ... did not contain other, potentially distracting, objects (fingers, sex toys, piercings etc.) and were hairless to account for current fashion.

They showed their pictures to 40 males. Most of the men were in their 20s, and they asked the participants about factors like their sexual orientation (they all reported themselves to be straight) and number of sexual partners. The men rated the attractiveness of each image.

The ratings of attractiveness were the exact opposite of those predicted by the signalling hypothesis. The reddest images were rated the least attractive.

The authors are then tasked to come up with an hypothesis as to why redness is less attractive. Their suggestion is that red is suggestive of menstrual blood. I'm not sure how one would test this hypothesis.

The results also showed that there was no difference in the judgments of men depending on their sexual experience. I learned from the Methods section of this paper that... shhhh, don’t spread this around... one can find pictures of female genitalia on the Internet. Is is possible that the men in this study knew this and might have looked at pictures of ladybits before participating in the study? I know, it’s incredibly unlikely, am I right? But if they did, it might explain why they found no difference in attractiveness ratings according to number of partners the men had.

This study is useful in that it tries to test an adaptive hypothesis experimentally. But it is frustrating because it is a limited study and hard to interpret.

First, there were few stimuli used. Only four pictures were used (then coloured four shades of red, for a total of 16).

Second, and more importantly, for an hypothesis that is all about sex, the authors seemed determined to make everything as clinical and detached and, well, unsexy as possible. First, the pictures were substantially cropped. They didn’t show the labia minora or the clitoris. (Correction; see comments.) As mentioned in the quote above, they didn’t want to use images had any sort of sexual nature (non-pornographic). The female equivalent of this task might have been to evaluate penises for attractiveness from pictures that only showed a flaccid member.

Perhaps not surprisingly, the men didn’t find images of lady parts alone to be very attractive. On a scale of 1 to 100, the average was around 40, except for the reddest, which was rated 35.

I’m curious as to whether the authors would expect to see the same effect with homosexual women.

Finally, there is a great opportunity for further research. The authors note:

Surprisingly little is known about the range of variation in morphology and colour of the external genitalia of normal women of reproductive age, however, and further research is necessary in this area.

I think this could be the chance for someone (not me) to create the best citizen science project ever. “Ladies, all you need to contribute to science is privacy and a camera.” We need data!

9 comments:

I'm a bit appalled by the protocol (hairless, really?) and surprised by the alleged difficulty of finding non-pornographic depiction of vulvas.Out of the top of my mind:http://www.showoffbooks.com/photos andhttp://www.cafebabel.co.uk/article/37610/copenhagen-kussomaten-vagina-photo-booth-interview.html

And what about the pigmentation issue? What skin (and mucosa) color were the subjects familiar with?

There's an argument to be that hairless could remove an extraneous variable, since hair colours could affect the perception of skin colours. To invoke "current fashion" seems strange thing when testing an hypothesis that is red is an evolutionary adaptation; such adaptations should be strong enough to override "fashion".

A similar argument might be made for skin colour. The Methods don't say, but I'm guessing all the samples were Caucasian.

I think you've misinterpreted part of the methods a bit. (I actually did exactly the same thing the first time I read it.) They didn't crop out the clitoris and labia minora from the images that they showed to the research subjects. They cropped them out, altered the cropped parts, then pasted them back in to the original image. This means that they weren't reddening the entire picture. This also might somewhat control for differences in skin colour because the changes in redness would be presented as relative to the skin around it.

Zen, regarding the "current fashion" bit (which yes I agree is a bit weird), they do point to studies that show that the amount of pubic hair shown in porn has decreased over time, but the colour of the genitals hasn't. So I think they're arguing that preferences for a certain grooming style are not an adaptation, but preferences for (or against) a certain colour are. Though they don't make that argument explicitly.

This was just plain weird. And I too was appalled by the hairless thing being "in fashion." It's simply not true and would be a silly variable to remove when testing an evolutionary hypothesis. Also, by the time you see a woman's external sex organs, aren't chances relatively good you will have at least some sexual contact? So I wonder how important it is for this part of the body to have selection operating on it.

A more prosaic guess would be that aversion to women with reddened vulvas might have something to do with the fact that pretty much all women's vulvas aren't really very red at all, even when highly aroused or even after considerable stimulation. And so a reddened vulva suggests not so much fertility or even promiscuity but some kind of inflammation. Quick way to test that hypothesis? Ask a bunch of men to react to images of the faces of women's with greater or lesser amounts of sunburn or allergies.

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As for hairlessness, while pubic hair removal is a recent fashion decision in contemporary Anglo-American and western European culture, in much of the world it's regularly practiced by both sexes for reasons of either religion or hygiene. Or both. And consequently isn't considered as titillating elsewhere as it is here. (In Europe see also merkins and the reasons men and women wore them in the 13th-16th Centuries.)

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I think the whole question is a bit daft. But as long as someone else brought it up my 2-bit hypothesis hypothesis for an "evolutionary" theory of men avoiding reddened vulvas would be that, as with some other primates, redness might indicate fertility. And contrary to what seems to be just about everybody in ev-psych, I hypothesize that men aren't as casual about actual reproductive sex as we're led to believe.

I suspect it's significant that the men in the survey were never shown images of their own partner's vulvas, red or not.

It would obviously be difficult to get past IRB, and there would be other difficulties, but a variation of the study I'd ask to see would be one where men were asked to rate their attraction to photos of their own partner's vulvas at different stages of fertility. And/or different states of "redness." I'd then compare this to their reactions to relative stranger's vulvas.

I'm not sure what the results would be, but I'm sure I wouldn't be comfortable speculating without that additional data.

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Oh yeah, and meanwhile I've balked at the whole 60s-era panoply of "evolutionary" proposals that red lips are proxies for red vulvas or that prominent breasts as replacements for buttocks. Without which "primitive" man would be just too stupid to have successful "mate" in the missionary position. Despite extraordinary emphasis by ev-psychs on sexual-behavioral evolution of women I'm given to understand that in many species males and females evolve at unsurprisingly similar rates.

Proxy for vulva or not, lips are painted red quite regularly. So the obvious thing to do would have been testing for the attractiveness of images of lipes in different hues. Could even be one and the same pair of lips photoshopped in different colours. If red hues turn out to be the most attractive, then the issue will be settled without even having to look further downwards.